Regulating apparatus for cracking stills



Aug. 31; 1926. 1,597,821

v D. PYzEL REGULATING APPARATUS FOR CRACKING STILLS rrOfP/vfys.

Aug. 31 1926.

D. PYZE] REGULATING APPARATUS FOR GRACKING STILLS Filed June 25 1924 2 Sheets-Sheet 2 Patented Aug. 31, 1926.

UNITED STATES PATENT OF F I C E DANIEL PYZEL, OF PIEDMONT, CALIFORNIA, ASSIGNOR TO SIMPLEX REFINING CCI-- PANY, OF SAN FRANCISCO, CALIFORNIA, A CORIORATION OF ICALIFORNIA.

'REGULATING APPARATUS FOR CRACKING STILLS.

appiication med June 25, 1924-. sum1 No. 722,296.

My invention relates to the art of cracking petroleum oils. In that art it is common practice to raise 'oils to and hold them at a cracking temperature, usually under some pressure, for the purpose of breaking up the oil and producing` from cheap and stable oils more volatile hydrocarbons such, for example, as gasoline. There are in use today a considerable number of forms of apparatus capable of cracking oil.

It is an object of my invention to prof vide means by which the capacity of such apparatus is greatly increased and the operation thereof simplified by providing means for automatically compensating for variable factors found therein.

Further objects and advantages will be made evident hereinafter.

Referring to the drawings which are for illustrative purposes only.

Fig. 1 is a diagrammatic elevation of a plant embodying my invention.

Fig. 2 is an elevation of the pump.

Fig. 3 is a section on the line 5-5 of Fig. 2.

Fig. 4 is a characteristic curve of the pump.

As illustrating one form which my invention may take I show it'applied to a cracking plant in which 11 is a furnace which is provided with suitable heating means such as a gas burner 12 and in which is situated a continuous coil,of pipe 13 forming a heating means. The upper end of the pipe 13 is connected through a pipe 14 with the top of an expansion chamber 20, this chamber being formed of metal and being of suiiicient strength to stand pressure, being perfectly heat-insulated. The upper portion of the eX- pansion chamber is connected through a pipe 21 with the lower portion of a dephlegmator 30. This dephlegmator consists of a tight shell 31 having pans 32 and 33 arranged alternately therein. The pans 33 have a central opening and the pans 32 are somewhat smaller than the interior of the dephlegmator so that an annular opening is left between the edge of the `pan and the wall of the dephlegmator. A vapor line 34 leads from the top of the dephlegmator 30 to a condenser 40. Raw oil is fed into the dephlegm-ator 30 `through a feed pipe 35, lthe oil being delivered thereto from a feed pump 50. The lower portion of the dephlegmator is connected into a regulating stand pipe 60. This stand pipe acts as a storage means for liquid leaving the dephlegmator 30 and is so referred to in the claims without intention to limit the term storage means to this actual embodiment.

The above apparatus is all well known in the art and is used very successfully in crack- Ying oil, the'stand pipe 60 being ordinarily connected to the inlet end 15 of the heating coil 13. When so connected the raw oil delivered to the dephlegmator by the pipe 35, after passing through the dephlegmator and having portions of its lighter contents vaporized therein, is delivered from the bottom of the dephlegmator to the regulating stand pipe 60. In its passage downwardly through the dephlegmator the oil collects certain heavy condensates from the vapor stream. The mixture of partially treated oil and condensate collects in the bottom of the dephlegmator and passes downwardly into the regulating stand pipe. In the previously constructed plants, themixture passes through the heating coil 13, and back into the expansion chamber 20. A

I have found that the operation of plants of this type is a ditlicult matter and that the capacity of such plants is small due to the fact that gravity alone is depended upon to force oil from the stand pipe 60 to the heating coil 13. The vapors produced in the apparatus are under such conditions of temperature and pressure that they are close to their critical temperature. As a result the latent 'heat of vaporization of such vapors is always the practice to support the dephlegmator on a high tower thus allowing for the use of a long stand pipe and providing for some variation in therateof production of condensates, the rate of flow to the, heating means increasing as the level of the liquid rises in the stand pipe and thus automatically increasing the removal of condensates from the dephlegmator.

This method of providing for automatic operation of the apparatus would .probably be satisfactory were it physically practical to elevate the dephlegmat'ors to a sufficient' degree. The specific gravity of the liquid in the stand pipe at its elevated temperature is probably about one-half that of water, however, and it is impractical to sufficiently elevate the dephlegmator to provide for the necessary wide variations in condensate production if the apparatus is otherwise operated to capacity. It is therefore the present practice to operate such apparatus at a low rate carefully watching and regulating this rate to prevent excessive production of condensate/ I have found that the capacity of apparatus of this type can be very greatly increased if I supply a pump which takes oil from the stand pipe 60 and delivers it under pressure to the inlet pipe 15 of the heating coil. It is impractical, however, to use an ordinary piston pump driven at a constant speed, for this purpose since where such a pump is used, there is very great liability of the pump drawing all ofthe liquid out of the stand pipe 60 and pumping vapor therefrom into the heating coil 13. This results in serious injury to the heating coil, since the presence of vapor in the heating coil prevents the heat delivered to the exterior -thereof which is ordinarily rapidly absorbed in the liquid therein, from being promptly carried away and the use of piston pumps for this purpose has been previously found to be impractical and dangerous. I have found, however, that by the use of a particular type of pump I am able to use forced circulation without danger and with excellent results.

I utilize the type of pump illustrated in Figs. 4 and 5, this pump consisting of a casing 71 having an inlet opening 72 and an outlet opening 73. A rotor 7 4 is mounted on a shaft 75 which is driven by a motor 76. Certain specific types of construction have to be adopted when handling very hot oil but these specific forms of construction forming no part of the present invention, need not-be referred to herein. The pump is of the centrifugal type. Pumps of this character have the characteristic of automatically reducing their throughput as the differential head against which they operate is increased.

In Fig. 4 I show a characteristic curve of such a pump in which distances on the line (0)-() represent values of the differential head against which the pump operates and distances on the line (0)-(y) represent throughput of the pump. AThe curve M N defines these values. If for example the head is reduced from (b) to (d) the throughput is increased from (a) to (c). Thus a small reduction in the differential head substantially doubles the amount of oil passing through the pump.` Also if the differential head is slightly increased from the value (b) yto a value represented l by the line O-M the throughput falls to zero.

In the apparatus shown, the differential head against which the pump operates is the head of oil in the pipe 14 plus the fricnoted that in the commercial operation 0f such pumps they are usually operated on that portion of the curve between the points (K) and (L). By operating the pum on the at or extreme left handportion o the curve'as shown it is possible so obtain the very desirable characteristics herein utilized. The method of operation is as follows: Raw oil introduced through the pipe 35 into the dephlegmator 30 flows downwardly over the pans 32 and 33 absorbing and condensing condensates from the vapors therein, and giving up to these vapors its constituent parts boiling at a point below the temperature ofthe dephlegmator. The mixture of partially treated oil and condensate flows into the stand pipe 60 and is delivered therefrom to the suction side of theI pump '70. The pump forces the mixturethrough the heating coil 13 and through the pipe 14 into the expansion chamber 20. The expansion chamber 20 is of sufficient capacity to allow the cracking reaction to complete itself therein producing vapors Which pass through the pipe 21 into the dephlegmator 30. In the dephlegmator 30 the vapors are sufficiently cooled to cause the stream of raw oil owing downwardly therethrough to collect and condense all the vapors of condensates boiling above a definite temperature. The remaining vapors of condensates having a lower boiling point pass through the pipe 34 and are condensed, to form the desired low boiling point condensates, in the condenser 40. The pump 70 automatically regulates the level of the liquid inthe stand pipe 60. Should the amount of-condensate formed in the dephlegmator increase for any reason the level is raised and the differential head against which the pump operates is accordingly diminished.. The pump has such special characteristics that a small reduction in the differential head greatly increases the rate of throughput of the pump and this throughput continues to increase rapidly as v tained.

If for any reason the rate of production of condensates is then reduced the level of liquid in the pipe 60 starts to fall and the differential head, a ainst which the pump 7 0 works, is accordingly increased. This rapidly cuts down the rate of thorughput of the pump and should the level fall below a certain critical point the throughput ceases. This, however, cannot occur in practice as long as any liquid is lowing from the dephlegmator 30 into the stand pipe 60.

It will be seen that, owin to the peculiar characteristics of the centrifugal pump 70 it is possible to automatically hold th'e level of the liquid in the pipe 60 within narrow limits even with wide variations in the rate at which liquid is supplied from the dephlegmat-or to the pipe 60, the pump 70 automatically increasing its throughput to compensate for an increase in the rate of supply and reducing its throughput to compensate for a decrease.

By the use of my invention apparatus of the character above described operates automatically under all conditions. Due to the fact that the pump 70`will automatically take care of large increases in the rate of condensate production in the dephle ator 60 it is possible to greatly increase t e rate at which raw oil is supplied and therefore to double and in some cases to treble the Capacity of a given plant.

I claim as my invention:

1. In an apparatus for crackin oil, the combination with a heating coil, o a reacting zone in communication therewith, a reflux condenser, means for delivering heated vapors from said reacting zone to said reflux condenser, a condensate storage receiver, means for delivering reflux condensate to said receiver, and mechanical pressure applying means acting in response to the level of condensate in said storage receiver for automatically forcing said condensate through the heating tube in a quantity varying with the level of condensate maintained in said storage receiver.

2. An apparatus for cra-cking oil, compris- I ing a heating coil, a reacting chamber, a reflux condenser 1n communication therewith means for delivering the vapors from said reaction chamber to said reflux condenser, a condensate receiver in which a quantity of refiux condensate is maintained, and a pump in communication with said receiver, said pump acting automatically in response to the level of condensate in said storage receiver for delivering condensate to the heating tubes in a quantity varying with the level of condensate in the storage receiver. 3. An apparatus for cracking oil, comprising a heating coil, a reacting chamber, a reflux condenser in communicationtherewith, means for delivering the vapors from said reaction chamber to said reflux condenser, a condensate receiver in'which a level of reflux condensate is maintained, and a constant speed pump in communication with said receiver, said pump acting automatically in response to the level of condensate in said storage receiver for delivering condensate to the heating tubes in a quantity 

